Ge/SiGe-based thermoelectric generator

Odia, Ameze (2017) Ge/SiGe-based thermoelectric generator. PhD thesis, University of Glasgow.

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Abstract

This thesis summarizes the milestones achieved in building a thermoelectric
generator (TEG) device using a novel p- and n- type 2-D thermoelectric material
called Ge/SiGe superlattice; which was grown by low energy plasma- enhanced
chemical vapour deposition (LEPECVD). It begins by describing in a nutshell the
advances made in the area of thermoelectrics since its inception in 1821, to the
present application of nanotechnology to develop state-of-the-art
thermoelectric materials of which the aforementioned material is one. Next,
characterisation of the Ge/SiGe superlattice using a combination of experiment
and Finite Element (FE) modelling is explained and the results obtained are
discussed in comparison with published experimental results. Thereafter,
experimental and FE results of the application of the Ge/SiGe superlattice to
fabricate a TEG device are presented and discussed. The experimental results on
the fabrication of Ge/SiGe TEG device is the first major success at achieving
practically feasible voltage output of up to 2.16 mV. For ease of comparison with
other published work, an effective Seebeck coefficient of 471.9V/K was
estimated. At impedance matched loads of 15  and temperature difference
measured across the device of 5.6 K, a power density of 0.111 W/cm2 and
thermal efficiency factor of 0.0035 Wcm-2 K-2 were also estimated. The results
though comparable to a few published works, still required further
improvements. The limitations of the TEG that resulted to the low
aforementioned performances were discussed; some of which include the
restriction of the TEG to a unicouple, having only one p- and n-leg. This
limitation is related to the development of the p-type Ge/SiGe material which
was identified during the course of this research work. Another major limitation
is that the improvised design of the unicoupled TEG, makes use of indium
bonding to connect the p- and n- legs electrically in series and thermally in
parallel. Indium has a low melting temperature of about 120ºC. Hence increasing
the heat source above this temperature will dislocate the legs. The consequence
of this is that the attainment of a significant temperature difference across the
TEG that will eventually result to a high Seebeck voltage, based on the Seebeck
effect principle, is limited.
Ways to address these problems were therefore discussed as recommendations
for future research work.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Ge/SiGe superlattice, thermoelectric generator, finite element (FE) modelling, unicoupled TEG.
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
Colleges/Schools: College of Science and Engineering > School of Engineering
Supervisor's Name: Paul, Professor Douglas
Date of Award: 2017
Depositing User: Mrs Ameze Odia
Unique ID: glathesis:2017-8174
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 12 May 2017 14:21
Last Modified: 10 Jun 2017 12:08
URI: http://theses.gla.ac.uk/id/eprint/8174

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